Evaluation of Phenotypic Characteristics of Sixteen Accessions of Sunn Hemp in Florida

Limited adoption of sunn hemp (Crotalaria juncea) as a cover crop in the U.S. is primarily due to the irregular supply and high cost of imported seed. Seed production in the continental United States would provide a more consistent supply of lower cost seed while also providing growers with a new seed crop. Improved availability and affordability of sunn hemp might encourage its utilization by growers in their cropping systems for weed and pest suppression, soil stability, and nitrogen and biomass accumulation. Sixteen accessions of sunn hemp were evaluated in 2008 and 2009 at Rosie's Organic Farm in Gainesville, Florida to assess their vegetative and reproductive characteristics and potential for seed production in Florida. The experimental design was a split plot with planting dates (May, June, and July) assigned to the main plots, which were arranged in a randomized complete block design with four replications. The sixteen accessions were randomly assigned to the sub-plots. Data were collected on plant height, leaf area, number of leaves, number of branches, plant weights, days to first open flower, and seed production. Field observations suggested that accessions could be separated into two distinct groups based on size and daylength sensitivity. Analysis of the vegetative and reproductive data provided evidence for one group of short-day accessions and one group of day-neutral accessions. The short-day accessions were taller, with higher shoot biomass, later branching and flowering than the day-neutral accessions, and little or no seed. The day-neutral accessions flowered early and produced viable seed in summer. Of these accessions, PI 314239 and PI 322377 produced the most seed, demonstrating potential for use for seed production in Florida. These accessions had the lowest shoot biomass, making them less desirable as a cover crop. Future work will focus on developing day-neutral cultivars of sunn hemp that retain the cover crop attributes of the commercially available short-day sunn hemp varieties, but are capable of producing seed in Florida.